The present invention relates generally to the field of communication systems, and more particularly, to a method of routing a voice call to a mobile station that is engaged in a packet data call.
The Code Division Multiple Access (CDMA) IS-2000 network supports concurrent services functionality (packet data and voice). In particular, a mobile station (MS) operating in the IS-2000 network may be in a state where it is engaged in a packet data call and simultaneously available for voice originations and terminations. If the MS has undergone an intersystem hard handoff (HHO) prior to entering this state or an intersystem HHO occurs while the MS is in this state, the MS will not register with its serving mobile switching center (MSC) as long as the data call remains active. When this occurs, delivery of mobile terminated voice calls to the MS is complex and may lead to excessive intersystem messaging. For example, an anchor MSC could send ANSI-41 intersystem setup messages to a list of MSCs that might be serving the MS to setup the call. Those not serving the MS would reply with a setup result of xe2x80x9cunsuccessfulxe2x80x9d. However, it is unclear how the MSC would determine the members of the list. FIG. 1 illustrates the problem of the delivery of mobile terminated voice calls after an intersystem HHO has occurred.
As shown in FIG. 1, the MS 118 is engaged in a packet data call with the PDSN 120. While the MS 118 is engaged in the data call, the originating MSC 102 receives a voice call attempt. The originating MSC 102 obtains the location of the MS 118 from the Home Location Register (HLR) 104 in the MS""s home network. The HLR 104 obtains the circuit address, specifically the temporary local directory number, of the MS 118 from the anchor MSC 106 and a circuit bearer path (physical circuit that carries the bearer data) for the voice call is established to the anchor MSC 106. The anchor MSC 106 is the first MSC that the MS 118 registers with. The MS 118 receives access network management and control from the anchor MSC 106 via the Base Site Controller (BSC) 108 and Base Transceiver Station (BTS) 109. When the MS 118 undergoes an intersystem HHO, a different MSC shown as a first serving MSC 110 will begin xe2x80x9cservingxe2x80x9d the MS 118. The MS 118 will now receive access network management and control from the first serving MSC 110 via the BSC 112 and BTS 113. However, the MS 118 will not register with the first serving MSC 110 as long as the data call remains active. As designated by the dotted lines in FIG. 1, the anchor MSC 106 may not have the Signaling System 7 (SS7) address of the first serving MSC 110 and may not have a bearer path to deliver a voice call to the first Serving MSC 110. (The SS7 address is what the MSC uses to address signaling messages to other network elements.) Thus, the MS 118 will be unable to communicate with the first serving MSC 110 via the BSC 112 and BTS 113 for receipt of the voice call. The problem continues if yet another HHO occurs to a second serving MSC 114. Again, the anchor MSC 106 may not have the SS7 address of the second serving MSC 114 and may not have a bearer path to deliver a voice call to the second Serving MSC 114 via the BSC 116 and BTS 117. Currently, Chapter 5, Section 6 of Cellular Radiotelecommunications Intersystem Operations (ANSI/TIA/EIA-41-D), hereinafter referred to as ANSI-41, defines messaging that can overcome this problem for most mobile terminated voice call delivery scenarios. However, the messaging is complex and may not be available on all MSCs. A copy of ANSI-41 may be obtained via a world wide web site located at www.tiaonline.org, or by writing to Telecommunications Industry Association, 1300 Pennsylvania Ave., Suite 350, Washington, D.C. 20004 USA.
Thus, there is a need for a method of forcing a MS to re-register its location after an intersystem HHO without significantly impacting ongoing data sessions to eliminate the need for current complex processing. Such a method would allow routing of a voice call to the MS while the MS is engaged in a packet data session.